This invention relates to the delivery of temperature and vapour level controlled gases to a delivery point.
The invention has particular, but non-exclusive, application in relation to humidifiers for use in the medical field and it is herein described for convenience of reference in this context.
When a normal person breathes atmospheric air his air passages supply heat and moisture to the inhaled gases, the body being capable of supplying the required amount of heat and moisture. However under certain conditions in medical practice a patient's mechanism of supplying heat and moisture is interfered with, and it becomes necessary to provide an artificial means for warming inspired gases to a point at or near normal body temperature (37.degree. C) before the gas is delivered to the patient. Similarly, it is necessary to humidify the inspired gases to a level at or near full (100%) saturation.
Temperature and vapour level controlled air might typically be required to be delivered to a shocked or very ill patient, to a patient whose air passages have been bypassed by a tube or tracheotomy for artificial ventilation, to a neonatal patient (who has a low reserve of heat and moisture) undergoing intensive care, or to a patient who is subject to prolonged breathing of cylinder stored compressed gases.
Apparatus which is currently employed for the conditioning of gases to be delivered to a patient generally takes the form of either a so-called nebuliser or a heated humidifier. Nebulisers function to produce fine water droplets in a heated gas suspension, by a process of atomisation but they are known to have serious disadvantages. Heated humidifiers function by supplying heat and moisture to a gas by the passage of the gas through or over a heated waterbath or evaporative surface.
The heated humidifier type apparatus is currently manufactured in one or other of two forms (vis., a simple humidifier or a heated hose humidifier), but each has its characteristic disadvantages. In the simple humidifier gases are saturated with water vapour by being passed over heated water within a tank humidifier chamber and are then fed to a patient by way of a flexible hose. Considerable heat losses to atmosphere occur during passage of the gas through the hose and, in order to obtain a delivery temperature at or near body temperature, it is necessary to heat the water in the humidification chamber to a much higher temperature than that required by the patient. This results in heavy condensation along the hose length and, unless the condensate is cleared from the system a potentially hazardous situation is created.
To overcome this problem heated hose humidifiers have been developed in which the delivery hose is itself heated to maintain the temperature of gases delivered from the humidifying chamber above the dewpoint. In this case the chamber is operated at a constant temperature which corresponds to that required by the patient and as the hose is heated to a slightly higher temperature, condensation within the hose is avoided. However, it is characteristic of such apparatus that the humidifier itself is run at or near normal body temperature and because a simple tank humidifier will not produce vapour at above approximately 80% saturation at the gas flows involved, a much larger than normal evaporative surface inside the tank is required. This has involved the use of a complicated structure to provide the necessary evaporative surface inside the tank and such a structure is inevitably relatively difficult to service and clean.
It is an object of this invention to provide a gas conditioning apparatus employing a humidifier tank which is easier to service and clean than prior art apparatus.